My sister’s little secret (part 3)I knew my sister was getting a bit kinky when she asked me to provide a sperm sample for her human biology homework….She approached me one afternoon and, as usual began to undress, teasing me with her slow strip, and finally revealing her bush of curly vaginal hair, as she slowly peeled of he panties. By this time my well-trained cock had hardened up and by the time I removed my shorts it was standing out stiff, a bead of clear ooze emanating from the slit.She always started by fondling my balls with her fingers, gently rolling the eggs in their sack, her fingertips stroking them and this invariably produced dribbles of gooey precum, that hung from my cock like silken threads….All the while I would be slipping my fingers into her vagina, enjoying the slippery hot tightness of her forbidden musky wetness.During our session, she said, “I need a fresh sperm sample, so that I can study it under a microscope – we’re doing the human reproductive system at school, and I’m probably the only one with access to fresh semen!”“No problem” I chuckled, “As long as you are prepared to collect it, I’m happy to squirt it out!”“There’s just one thing” she said, “We are working in pairs, so my friend Tina will be a part of the study” and then before I could speak she said, “It’s OK, she wants to see how a penis ejaculates”I was stunned “So just exactly are you suggesting?”“Well, you could lie on the bed, güvenilir bahis and Tina and I could masturbate you, and collect a semen sample, and we could put it under the microscope, and see the little tadpole thingies swimming around”This was weird, but I was getting turned on by the idea, but I needed to get something in return, not just a quick wank so I said “OK, but only if can watch Tina and you masturbate first, and you have to be completely naked, and do it slowly” and I added, “It will make me cum a bigger amount, also, you must both promise to NEVER EVER tell anyone about this!”So on a day when we knew that our parents would not be back till late, my sister arrived from school with Tina, and a box containing a microscope, which they set up in her room. It was awkward at first, we were ally self-conscious, but eventually we all began to undress in my sister’s room making sure that the door was bolted.I lay back on the bed and watched Tina undress, she had perky tits and large fleshy vaginal lips, and a deep slit, and her pubic hair was fine and silky. When she pulled her lips apart, her pink wetness was evident, she was obviously getting turned on by the whole situation, and her eyes never left my swelling cock as I began to slowly rub my hand up and down my foreskin, exposing the glistening purple head.The girls, squatted facing me, and giggling at the scene, both began to masturbate, watching me, and türkçe bahis glancing at each other, self-conscious at first, but eventually getting into the action, faces flushed as they grew more intense. Tina came first, bucking and gasping, her eyes still riveted to my cock which was oozing with slippery lubricant, and I could make out her erect clitoris poking out of it’s fleshy sheath.My cock was throbbing painfully, my balls were tight as my scrotum contracted, awaiting the release of built-up spunk that I knew was going to happen…My sister inched towards me, and I reached slipped my fingers into her pussy, as she worked her clit in semi-circles with her fingers, faster and faster, and I brought my fingers up to my nose and inhaled her musky scent before licking the dripping slippery juice.Tina moved up and slid her pussy-flavoured fingers into my mouth, and I licked greedily tasting her salty, slightly bitter ooze. She wrapped her hand around my dribbling cock and began to squeeze it, and I gasped as she caused a slippery dollop of precum to leak out.“Don’t make him shoot, we’re supposed to be collecting his sperm!” my sister said. “I know, but I couldn’t resist having a feel” Tina replied, as I felt my cock throbbing with anticipation.My sister reached her orgasm, her vaginal contractions sucking at my fingers and coating them with hot juices, and after recovering, she got off the bed and returned with a latex güvenilir bahis siteleri glove. “We’ll collect his sperm in this” she said, “you won’t believe how much he shoots out’Tina giggled, still focused on my cock “Looks like you two do this sort of thing regularly”“We like to play mummies and daddies now and then” my sister chuckled, “here you go Tina, you rub it, and I’ll get ready to collect the semen, and YOU …” she said staring sternly at me, “had better tell us when you’re going to squirt, I don’t want your sticky stuff all over my bed!”So I lay back, as the two girls worked on my cock, Tina’s soft hand sliding my foreskin back and forth over my glistening purple head, and my sister massaging my balls, and rubbing the pulsing cock root underneath.It took hardly any time before I croaked in a strangled voice “I’m cumming, oh God, I’m cumming!” and I felt the spunk begin to build up behind my balls … the girls squealed with excitement and my sister slipped the glove over my pulsing cock, as I shot squirt after squirt of hot thick white baby batter into the glove. She milked the last of it as I bucked and groaned in ecstasy, and held it up with a triumphant grin.Tina’s eyes were glazed with excitement, and I knew we’d repeat this little get-together soon, but my spent cock was softening and dribbling the last of it’s offerings onto my belly, as the girls made their way to the microscope with their glove, it’s fingers distended with my cum. I got up and left the room to go and have a shower, I could hear them giggling “Hey, look at all the little tadpoles swimming!” as they poured over the microscope.I was just happy to do my bit for science!